The invention relates to a method for drying a paper web, especially fine paper or newsprint, in a paper machine wherein the paper web to be dried is passed over a mantle face of a large-diameter flow-through cylinder on which a set of drying-gas jets is applied to a free outer face of the web through a nozzle arrangement. Water is evaporated outward from the outer part of the web by means of the set of drying-gas jets. The water vapor thus evaporated is removed through spaces in a blowing-on hood. By means of the set of drying-gas jets, the interior of the web to be dried is also heated.
Further, the invention also relates to a dryer for paper, in particular for fine paper or newsprint, intended for carrying out a method of the invention. The dryer of the present invention comprises a flow-through cylinder and a blowing-on hood arranged above the cylinder. The hood is provided with a nozzle arrangement by means of which a set of drying gas jets can be applied to the outer face of the paper web to be dried while the paper web is being passed over the flow-through cylinder.
In prior art devices, paper, such as newsprint and fine paper, is dried in a multi-cylinder dryer, which comprises a large number of drying cylinders arranged in one row, or in two rows placed one above the other. In the drying operation of tissue paper, in prior art devices, so-called Yankee dryers are utilized. These Yankee dryers comprise a large-diameter heated cylinder on which a so-called blowing-on hood might be arranged. Inside this hood, a large number of nozzle pipes are arranged. Drying air jets are applied through these pipes to the free web face at a high velocity. The mantle of a Yankee cylinder is preferably solid and unperforated, and it is usually a steam-heated pressure vessel. In a conventional blowing-on hood, evaporation of the water in the web takes place in one direction because the water cannot be evaporated towards the smooth face of the Yankee cylinder.
The water evaporation capacity of a prior art cylinder dryer per unit of area of cylinder face is about 15 to about 30 kg/h/sq.m. The corresponding evaporation capacity of a Yankee dryer provided with a blowing-on hood is about 100 to about 150 kg/h/sq.m.
Some drawbacks of prior art multi-cylinder dryers include the high cost of the construction of the dryer and above all the abundant and enormous space required by the dryer in the machine direction. Another drawback is the literally complicated draw of the web through the dryer which is susceptible to disturbances.